Electrical cables have been used as electrical interconnects in a wide variety of data and power transmission systems. Traditional electrical interconnect cables utilize conducting wires separated by a low-loss dielectric material. Example types of copper-based electrical interconnects include coaxial cable and twin-axial (“twinax”) cables. Direct-attached copper (DAC) cables are widely used in data centers for intra-rack connections.
Traditional wire-based cables suffer from frequency-dependent loss caused by a combination of skin effect, dielectric loss and roughness loss. Dielectric loss is due to the dielectric material (typically, a polymer) used to hold and separate the conductors in the cable. While low-loss dielectrics such as PTFE (Teflon) or even foams are used to mitigate the dielectric loss, they cannot completely eliminate this source of loss.
The skin effect is a fundamental phenomenon that affects all conductors and cannot be avoided. At high frequencies, the current that carries the electrical signals travels in a thin layer called the “skin depth,” measured from the surface of a conductor. The higher the frequency, the thinner the skin depth, with the skin depth being inversely proportional to the square root of signal frequency. As a result, the resistance of a wire—and consequently, the loss—increases with frequency. It would therefore be desirable to have an electrical interconnect cable that could reduce at least one of these loss mechanisms in order to have improved (higher performance) electrical connections, especially in view of the increasing need for high-frequency (i.e., high data rate) transmission.
Another limitation of conventional electrical interconnect cables is the transmission of both high-data-rate data signals and power signals over the same cable because the losses are too large. Consequently, separate cables are used, one for the data signals and another for the power signal. It would therefore be desirable to have an electrical cable that overcomes the loss problems and that allows for transmitting both data and power signals over the same electrical interconnect cable.